1. Field of the Invention
The present invention relates to liquid crystal-based video and graphics display devices, and, in particular, to increasing manufacturing yields for such display devices.
2. Description of the Related Art
A substantial need exists for various types of video and graphics display devices with improved performance and lower cost. For example, a need exists for miniature video and graphics display devices that are small enough to be integrated into a helmet or a pair of glasses so that they can be worn by the user. Such wearable display devices would replace or supplement the conventional displays of computers and other devices. In particular, wearable display devices could be used instead of the conventional displays of laptop and other portable computers. Potentially, wearable display devices can provide greater brightness, better resolution, larger apparent size, greater privacy, substantially less power consumption and longer battery life than conventional active matrix or double-scan liquid crystal-based displays. Other potential applications of wearable display devices are in personal video monitors, in video games and in virtual reality systems.
Miniaturized displays based on cathode-ray tubes or conventional liquid crystal displays have not been successful in meeting the demands of wearable displays for low weight and small size. Of greater promise is a micro display of the type described in U.S. Pat. No. 5,596,451 of Handschy et al. (digital pixel driver) and in European patent application no. 98122934.7 of Walker et al. (analog pixel driver), the disclosures of which are incorporated into this disclosure by reference. This type of micro display includes a reflective spatial light modulator that uses a liquid crystal (LC) material as its light control element. Typically, a ferroelectric liquid crystal (FLC) material is used as the light control element.
When manufacturing the spatial light modulator of the LC-based micro display just described, internal short circuits can develop that lower manufacturing yields, thereby increasing production costs. In order to keep yields high, it is necessary to insure that shorts between the transparent electrode on the cover glass and the top metal on the edge of the spacial light modulator chip will not have adverse circuit consequences,. Previous solutions to this problem have involved connecting this metal to the driving circuit for the transparent (typically made of ITO (Indium Tin Oxide)) electrode, or leaving this metal completely floating. However, the first solution can cause ESD (electrostatic discharge) damage to the ITO circuit, as well as shorts to ground, while the second solution violates manufacturing assumptions required for consistent plasma etching of the metal.
Thus, it can be seen that modern spatial light modulator manufacturing techniques impose manufacturing yield and production cost limits upon LC-based micro displays, and hinder the use of these micro displays in many applications.
Therefore, there is an unresolved need for an improved spatial light modulator manufacturing technique that can increase LC-based micro display manufacturing yields and lower production costs.